In the field of photographic processing it is well known to replenish processing solutions to compensate for loss of developer components by consumption by the process and aerial oxidation. Such a replenishment system requires replenisher pump(s), pipework and control means, all of which adds to the cost of the machine. Also, the control systems have to be calibrated to get constant sensitometry. In order to allow for errors in the calibration, the replenishment rate is often fixed at a relatively high rate. This means that much solution is wasted and is sent to a drain or an effluent tank for later disposal.
Some processing machines can be supplied by premixed solutions that are usually run until they produce unacceptable results and are not replenished hence avoiding the replenishment system described above.
U.S. Pat. No. 5,176,987 describes a method of developing a color photographic material that requires reduced developer replenishment by controlling the composition of the silver halide and the developer.
The problem experienced with such machines is that the quality of the images produced will deteriorate with continued use of the same solution. This means that the processing solutions must be discarded at a comparatively early stage if unvarying high quality processing is desired.